Selecting impulse transmitter



Sept 11, 1945. 1.. M. POTTS SELECTING IMPULSE TRANSMITTER Original Filed Feb. 1, 1941 2 Sheets-Sheet l STOP TART l I 2 3 B 2 FIG.6 c

INVENTOR. LOUIS M. POTTS AT R NEY Sept. 11, 1945. 1.. M. POTTS 2,384,558

SELECTING IMPULSE TRANSMITTER Original Filed Feb. 1, 1941 2 Sheets-Sheet 2 HO. 4 l8 FIG. 3

INVENTOR. LOUIS M. POTTS A OR'NEY Patented Sept. 11, 1945 v SELECTING IMPULSE TRANSLH'I'I'EB I Louis M. Potts, Evanston, 111.,

type Corporation, Chicago, 111.,

Delaware Orl asalgnor to Telea corporation of ginal application February 1, 1941, Serial No.

376,962. Divided and this application January 26, 1943, Serial No. 473,583

3 Claims. (Cl. 177-680) The present invention relates to dialing apparatus for station selection systems and more particularly to this class of devices adaptable for use with start-stop communication systems;

' This application is a division of U. S. applica- 5 tion Serial No. 376,962 filed February 1, 1941.

A principal object of this invention consists in providing dialing mechanisms operable after the manner of automatic telephone switching apparatus but capable of reproducing pulsations that may be repeated through start-stop telegraphic apparatus of the code combination Baudot signal class and which will be effective to actuate station selecting equipment automatically in order to establish communication between calling and called subscribers stations.

The use of station selection methods by means of manual dial equipment is equally desirable in printing telegraphy as it is in telephony. From a convenience and utility viewpoint it is proposed in accordance with the present improvement to so regulate standard dial apparatus by means of telegraphic regulating and periodicity safeguarding equipment as to make its use in conjunction with start-stop telegraphic systems equally practical. Toward this end a mechanical tie-up is effected between the dial apparatus and a startstop regulated shaft of a keyboard transmitter whereby a station selecting dial of standard construction as known in telephony is utilized for generating a number of permutation code signals which are composed of but a single line change characteristic during the entirety of the code combination so as to reproduce a number of similar signal impulses which may thereafter be used to operate station selecting switches after the manner of standard telephone practice.

In carrying out this plan of operation, the permutation code signal for the letter M has been chosen because it is composed of three successive spacing impulses followed by four successive marking impulses simulating thereby an average length of dialing impulse for operating a station selection switch. Since start-stop apparatus is, in fact, employed for the purpose of generating these dial type signals with the dial equipment serving only as a means of initiating the startstop equipment-and determining the number of signals, there is in effect produced a step-by-step pattern of signal which is also in fact a startstop signal and may therefore be received by start-stop apparatus such as tape transmitters, regenerative repeaters, etc., without impairment or need for auxiliary apparatus to insure against improper responses.

In attaining the above and other objects of the present invention, the principal embodiment described hereinafter utilizes a rotary dial mechanism operatively associated with a standard embodiment of start-stop permutation code transmitting keyboard. The dial may be operated manually by means of rotating a disc which is advanced by a finger movement until a predetermined mark or flngerhole thereof attains a stop. The disc is thereafter released and automatically responsive mechanism restores the disc to its normal position one step at a time. As each step is completed, and since a particular key lever of the transmitting keyboard is held depressed during such operation, there is obtained the transmission of a number of character M signals corresponding to the selecting index numeral which was dialed. Thus, if a destination selecting index is comprised of, say, six impulses the particular key lever and the transmitting apparatus are accordingly operated causing to be generated six permutation code signals of a particular letter, which accordingly constitute that number of station selecting impulses in succession. These impulses are received at a central station whereat they are effective to operate selecting switches to select an ultimate destination line over which start-stop messages may then be transmitted to a destination station.

The keyboard mechanism at each subscriber station is of standard arrangement and one of its character keys is depressed for a period of time commensurate with the degree of rotation of the calling dial at the same time the transmitter clutch is engaged for a corresponding number of cycles and as each character code is transmitted the dial is stepped back toward zero position. when the station calling dial reaches its zero position the transmitter is declutched, the key which had been held down is permitted to resume its normal condition, and the transmission of code signals is arrested. Accordingly, it will be understood that the number of call signals generated through the intermediation of the keyboard mechanism will correspond with the angular position to which the calling dial is rotated and from which the calling dial is returned to its zero position.

For a more comprehensive understanding of the present invention reference may be had to the accompanying drawings and to the detailed specification following hereinafter wherein like reference characters designate corresponding parts throughout and wherein,

Fig. 1 is a circuit diagram featuring the cenpawl lever 23 pivot 21 advancing in a counterclockwise direc-,

tral station equipment for selecting a destination station by apparatus embodying the presentinvention;

Fig. 2 is a fragmentary front elevation of a start-stop signaling system keyboard apparatus having applied thereto a station selecting dialaccording to the present invention Fig, 3 is a plan' view'of the apparatus mus trated in Fig. 2;

Fi 4 is a side trated in Fig. 2;

Fig. 5 is a detailed rear elevation of'the rotary dial mechanism according to the present invention;

elevation of the apparatusillusdownwardly causing its about its pivot 36 which character I i denotes generally a rotary dial type of station selecting switch. Essentially this unit is comprised of a disc I! which is integrally associated with a stub shaft l3, Fig. 4, and is provided with the ten finger tip receiving apertures, one representing each numerical integer of the decimal series.

Shaft I3 is journaled in a bushing I 4 which in turn is secured within a central opening of an enclosure cue ii, the latter member, as best viewed in Figs. 3 and 4, being supported in an inclined position by means or a suitable Supp rting bracket l8. Within the case l5, shaft [3 carries integrally associated with it a ratchet wheel I! having teeth which correspond in number and disposition to the finger engagement openings 5'! of the finger wheel l2.

As with conventional telephone dials, the unit II is provided with a finger stop II. The latter member is here formed of an arm extension originating from lever I! that is rotatably supported upon said shaft l3. Stop I3 is rotatable through a slight angular distance as determined'by the limiting pins 2! and 22 against the former of which said stop I 3 is urged by a spring 23. Inte gral with lever I I are two ears indicated 24 and 25, Fig. 5, the latter of which pivotally supports a pawl lever 26 as at pivot 21 and the former of which provides an anchor point for a sprin 23.

the other end of which is hooked as at 29 to the uppermost extremity of said pawl lever 26. 1

. Pawl lever 26 is limited in its counterclockwise rotation about pivot 21 as urged by the afore-described spring 28 when its uppermost extremity encounters the stop lug 3| which in turn may also be integrally formed with the afore-described lever l9. Upon th rotation of lever l9 as when its finger stop extremity i8 is engaged during the final degrees of movement or finger wheel l2, will be moved bodily upward with sought, and the finger in: is rotated in a clockwisedirectlonasvlewedinmzand3mounterclockwise'as viewed inl'ias. 5 and '7. This move- ,ment causes disc I! and ratchet wheel "to be concurrently displaced to a significant angular position as .deteiitarm 34 ridesover a, cone spending number of iecth'in ratchet wheel IT, in-

dicative of the digit thus operated. Thefinger upon encountering stop piece l3 moves the latter member'a distance co to the space between stop pins II and '22 and thewithdrawn. Thereupon, lever l3, tension of spring 23 store-described, endeavors to return to its original position as illustrated in the drawings and in so doing, pawl 23 is carried tooth projection 32 to en- Sage the extremity 33 of bell crank 35 and to rock the latter in a counterclockwise direction, Fig, 4, motion is mildly resisted by the lever return spring 31. Pawl 2i continues to engage extremity 33 thereby holding lever 33-35 in its counterclockwise position (as viewed in Figs. 4 and 7) until arm I, integral with ratchet l1, returns to-cooperate with projection 33 to disengage pawl 26 from extremity 33, as will hereinafter appear.

The movement on the part of bell crank 33 is then immediately translated into a counterclockwise motion of the character M operating bail 38, Figs. 2, 4, and 7. As ball 38 is rocked in a counterclockwise direction, Fig. 2, its light acting return spring 39 becomes distended and its remote extremity 4| engages and depresses key lever 42 whereby there is generated, through the tion as viewedin Fig. 5 so that tooth 32 of pawl lever'26, the upper edge of which is inclinedas indicated in Fig. 5, encounters the extremity 33 of a bell crank lever 35, Fig. 4, there will result the clockwise rotation'of said pawl lever 26 about its pivot 21 and in opposition to the return spring 28 as it accordingly yields to the extending portion 33 of bell crank lever 3 Relterating, the finger wheel I2 is operated by inserting a finger into one of the dial openings 51 which is opposite a numerical digit corresponding to an identifying character of the station normal operation of the transmitter mechanism, a permutation code signal corresponding to the character M as this key lever is identified, Fig. 3.

A keyboard apparatus for transmittin signals of thetype illustratedincm've AofFig. eismore fully described and explained in U. S. Patent No. 1,595,472. For the purpose of explaining the application of the instant invention, it will sufilce to state that upon the operation of any one of the key levers such as the particular key 'lever M indicated by the reference character 42, there is code bars each one of which supervises the performance of an associated goose-neck lever 43, Fig. 2, while also as a result of the operation of any one of'said set or key levers there is effected a leftward movement on the part of common release bar 44, Fig, 4, the rotation ofa trip lever 45, and ultimately the release of a declutching element 46. In consequence of the release motion on the part of lever 45, clutch elements 41 and 43 are brought together so that a single cycle of rotation is imparted to the set of transmitting cams generally indicated 49, Fig. 3, but thereafter the cam assembly 43 is arrested by trip lever 45 acting on clutch trip 46 notwithstanding that any operated key lever is continuously held down. It is accordingly necessary, under conventional practice, that a key lever depression be repeated a number of times in order to obtain a number of character'transmission operations.

The principal is to control successively the operation ot-a set of goose-necks 43 each of which in turn controls an individual pair of contacts of a set which are arrangedin a parallel alignment. In addition to this utility, however, cam sleeve 4! in accordance with the instant invention performs a further purpose as will now be described. One of the cams of assembly 5|. Against the finger is" being under performance of cam assembly 49 r rides a follower roller 52 which, as best indicated in Fig. 2, is carried by one arm 53 of a bell crank member whose other arm 54 is pivotally connected to a pawl 55, the extremity of, which is indicated 56 in Fig. 5.

In consequence of the afore-described arrangement, as cam is rotated, there results a horizontal reciprocation of pawl '55 which, with its extremity 56 engages consecutively the teeth of ratchet wheel "causing the latter member to be rotated in a clockwise direction, as viewed in Figs. 5 and 7 (counterclockwise as viewed in Figs; 2 and 3) one step at a time. As each impulse or character M signal is transmitted during the rotation of cam assembly 49, so also by reason of the horizontal actuation of pawl 55 and through its engagement with ratchet wheel ii, there is effected a restoration of the finger wheel l2 one step at a time until the normal or zero position is resumed. 7

It will be recalled that finger wheel l2 when rotated in a clockwise direction as viewed in Figs. 2 and 3 is capable oi. a total movement corresponding to a certain number of composite digital movements each equal angularly to the distance between successive finger holes 51 of which there are ten in the conventional type of dial illustrated, and that the final degree of movement of any station selecting operation results, in addition to the rotation of finger wheel l2, in the movement of finger stop i8 through a limited distance as represented by the two stop pins 2| and 22. When the operators finger is withdrawn, finger stopl8 being urged by the return spring 23 immediately seeks to resume the position as indicated in Fig. 5 whereat it rests against the stop pin 2|. It is to be noted that during the operation of finger stop member it when it was rotated counterclockwise (Fig. 5) pawl 32 through its articulation at pivot 21 with an ear 25 which is integral with arm I! is caused to be moved upwardly until its shoulder portion 32 overtakes the extremity 33 of bell crank lever 35. In passing over this extremity spring 28 yields sufiiciently to permit said pawl 26 a slight clockwise movement about pivot 21 but after its shoulder 32 comes into the clear again pawl 26 resumes its relative position to arm N as indicated and shoulder 32 is placed above said extremity 33 of bell crank 35 awaiting the release of finger piece 18.

As a result of the influence of spring 23, when the operators finger is removed, the entire assembly including arm l9 and pawl 26 are rotated clockwise, Fig. 5, as before stated. Shoulder of pawl 32 now positively engages the extremity 33 of bell crank lever 35 and causes the latter member to be rocked coimterclockwise about its pivot 36 as viewed in Fig. 4. Presently stop arm l9 encounters the limit pin 2| and its movement is thereat arrested determining thereby the extent of rotation of bell crank 35 which rotation is opposed by the return spring 31. In consequence of the counterclockwise rotation (Fig. 4) of bell crank member 33-35 its farthest extremity which underlies one arm 64 of the bail lever 38 causes said arm to be raised against the tendency of a return spring 39, Fig. 2, eifecting the depression of its key lever actuating extremity 4| as well as the rotation of its transverse bail portion 59. At the end of bail portion 59 uppermost in Fig. 3 there is integrall formed a trip arm 6! which carries the adjustable screw 52 for engaging the horizontally extending lug 63 as indicated also in Fig. 4.

In consequence of the operation of lever 33 there are eilected two results. Firstly, key lever 42 is depressed, effectively reproducing the manual actuation for transmitting the alphabetical character M and secondly the clutch trip 45 is rotated which results in the release of spring actuated driven clutch member 43 so that it comes into engagement with clutch drivin member 41.

In accordance with the conventional operation of keyboard telegraph transmittin apparatus such as the type illustrated in U. 8. Patent 1,595,472, the continued depression of any key lever such as the key lever 42 may not result in the transmission of any more than one character signal. In other words, to eiiect the transmission of a number 01' character signals it is necessary to depress any key lever and to permit the same to resume its normal position a number of times corresponding to the number of signals to be transmitted. This safeguard is usually obtained by the provision 01' a trip release mechanism in connection with clutch 41-48. It is now proposed by providing the extension Bl of bail 38 and by withdrawing clutch trip 46 at the same time that key lever 42 is depressed to permit cam assembly]! to rotate a number of revolutions corresponding to. the number of character M signals which are desired.

As cam assembly 4! efiects one revolution after another, its cam 5|, Fig. 2, encounters follower roller 52 and rotates bell crank 53 clockwise in opposition to its return spring 88, and as these operations proceed successively the downwardly extending arm 54 oi said bell crank causes the pawl 55 to be reciprocated to and fro. With each rightward movement of pawl 55, Fig. 7, leftward as viewed in Figs. 2 and 3, a succeeding tooth oi ratchet wheel 11 is engaged and then pulled forward thereby causing the finger wheel l2. to be restored by clockwise rotation, Figs. 5 and 7.

when the normal or zero position of finger wheel i2 is ultimately attained arm 61 which is carried integrally with ratchet wheel l1 engages I the projection 68 of pawl 26 causing the latter 33 01' bell crank lever 33-35 permitting the latter member under the influence oi its restoration spring 31 to resume its normal position as indicated in Fig. 4. In consequence ball 38 is free to resume its normal position under the influence of spring 3! whereupon bail extremity ll is withdrawn from key lever 42 and extremity BI is withdrawn from the horizontal plate 63 of clutch trip 4.. H

In this manner there is eflectively reproduced, by the use of a telephone station calling finger wheel l2, a system of transmitting a number of permutation code character M signals corresponding to the call number of impulses in a station selecting signal. As the station selecting signals emanate from the transmitter apparatus, generally indicated 68 in Fig. 1, they may, before arriving at the central ofiice 69, be regenerated at a repeating station such as the one indicated 1|. Typical repeating station apparatus is illustrated in U. S. Patent 2,104,273 and since the station selecting impulses are, in fact, a number of similar start-stop permutation code signals issued in series, they may be repeated over conventional start-stop apparatus such as illustrated in this disclosure without distortion.

Attention is directed to curves B and C of Hg. 0,-wheee-there-is shown respectively minimum and maximum peak ortolerance char-- acteristics ofa dial'signaling equipment auchaa isconventionalbiemployed in Test observations have indicated that any dialing signal having a spacing, characteristic smaller thanthatindicatedincurvehoronelargerthan' thatindicatedmcurvecislikelytoproduce false in station selecting switches of this type. According y. and since live unit per-. mutation code signals of the yp illustrated by the curve A are receivable in standard telegraph equipment, it has been found expedient to utilise a particular code combination which in accordance with convention has been assigned to the alphabetical, character II which signal is indicatedbythecurveDtobe'utilisedinthepurpose of reproducing station selecting impulses of the type necessary in operating telephone switching equipment. The spacingcharacteristic oi the code combination for letter K will, .as may be noted bycomparing curveDwith curves B and C, constitute aspacing impulse greater inlength thanthe minimum curve B and yet one which is less than the maximum impulse curve C. In composing the station selecting impulse of three code impulses contiguously arranged including the start impulse, it may be noted that a total length of spacing current, somewhat in excess of a median signal length, is thereby obtained. By observing curve D in comparison with curves B and one may notice that a two code impulse signal, which corresponds according to custom with the code combination for the character V, is also usable as a station selecting switch operating impulse if preferred.

There will now be described briefly the circuit of Fig. 1 to illustrate the application of the present invention in the embodiment discussed above comprising a central station and a limited number of outlying stations. The reference character il designates a transmitting station which may be a unitary apparatus of the type illustrated in U. 8. Patent 1,632,297 or of the ype illustrated in U. 8. Patent 2,177,077. "This outlyin station in addressing the central oiiice is may transmit its signals over a line in which is located a repeater apparatus II which may be of the type shown in U. 8. Patent 2,105,173 or of the type shown in U. 8. Patent 2,104,273. Either of these classes of repeater apparatus partalres of the characteristic of signal regenerative repeater,

that is, signals received from the outlyin station I are duplicated and retransmitted from a battery local to the regenerating station 1i and in this manner distortion efiects caused by conditions inherent in the line are eliminated by a well-known practice of reconstructing the original signals under the control of the transmitter ll so that as they enter upon the succeeding line directed to the central station the true theoretical signal pattern is again produced.

At the central station the incoming line passes through the winding of a slow-to-release relay 1!, thence over local line ll, contactor l3 and its normal make contact point l5, through the winding of relay It, to ground. As a result of normal marking current on the line, relay 1! will become energized and remain in its attracted condition notwithstanding the signal interruptions due to the succession of line selecting impulses comprised of a series of character M code combination signals, but relay it will intermittently release and attract its armature ll causing the latter element to be actuated from its front cmtactpolntlltowarditsbackcontactpoint llandvlceversa.

Asaresultoftheenergizationofslow-toreleaserelaylither willbedrawnupitsarma- -tures ii and 82, the former receding from its back contact point 01' and enga ing its front contactpoint ,whilethelatterwillbe attracted to its sole frontcontact. As a result of the closure of armature I! with its front contact a circuit will he established for the station selecting switch magnet 00, traceable from grounded front contact point II of relay it through armature ll, conductor 81, armature 02, its front contact of relay II which is normally energiud, conductor to the junction point ll, conductor ll, winding of magnet 00 to grounded As a result of the operation of magnet 00 intermittently under the control of received signals the station selecting switch will be rotated in a step-by-step manner advancing the three wiper brushes, SI, and so that they successively engage the contact points it, 01, and SI, respectively, after the manner of station selecting switch operation more-thoroughly explained in Kemps'ter B. Millers book of American Telephone Practice, fourth edition, Chapter XXXIV, published 1905.

As operating magnet 86 is alternately energized and de-energized in response to the fluctuations of armature II, the station selecting switch will advance its above recited wiper brushes until they attain a position corresponding to the number 01' station selecting impulses received, whereupon the station selecting switch will momentarily come to rest with one of the contact points ll aged by its wiper SI for a period suiiiciently long to cause the operation of slow-to-operate magnet 9!. This is traceable over an obvious circuit from grounded battery ill, winding of slow-to-operate relay 9!, line ill, wiper l5 and a particular one of its contact points 88, to the grounded bridging circuit Ill. As a result of the operation of relay 98, its two armatures ill and I0! will be attracted, the former coming into engagement with the contact point of contactor 13 and establishing a circuit for connecting the incoming line to the destination station, at the same time withdrawing contactor I! from contact point I! after the well-known manner of make before break switch operation.

contactor [l5 engaging contact point I" completes a circuit for maintaining energized the station selecting operating magnet 85. This circuit is traceable from grounded battery 92, through the winding of rotary switch operating magnet it, condutor 9| to the junction point 0!, thence over conductor 88, front contact of armature 02, conductor 81, armature II, (which is now released) contact point 18, contact point I" and its armature "5 (which is now attracted) conductor Ill, contact point 84 to grounded armature 8| (which is still attracted because normally current is flowing in the line). When contactor i3 is withdrawn from contact point l5 as above described, there results the de-energization of relay 1. As a result of the attraction of armature I" with the contact point of contactor I3 incoming line through the winding of relay l2 and local conductor 14 is continued over the contact point of contactor l3 and its associated armature Ill, conductor I08, wiper 9i and one 0! its contact points corr sponding to the selected station, thence out over one or the line conductors III to a particular destination station H2, 2A, etc.

After the communication with the destination station H2, 2A, etc., has been completed, the conductor may be broken at any point either between the central station and one of the destination stationsor between the calling station 68 and the central station, and the apparatus will become restored to zero or normal condition in the following manner. Slow-to-release relay 1!, being in circuit at all times, when the current is interrupted for a sufiicient length of time to de-energize said relay its armatures 8| and 82 will be permitted to fall back removing ground at armature 8| from the circuit which had been holding energized the switch rotary magnet 86 as afore-described whereupon the armature H3 will be permitted to recede and come into engagement with its contact point I ll. 'I'hereupon ground will be introduced again to the circuit including winding of magnet 86 as follows: from grounded battery 92, through the winding oi magnet 86, conductor 9|, armature H3 and contact point H4, conductor to the bridging circuit of the several contact points 91 and wiper 94, thence conductor H6, contact point 83 to grounded armature 8|. As a result magnet 86 will become energized again attracting its armature H3 away from contact point H4 whereupon the circuit will again be broken for said magnet 86 which will again release its armature I I3, -etc., the operation continuing intermittently until wiper 94 resumes the normal position at which it engages the zero contact point III which does not connect with conductor I I5. Since magnet 86 operates all of the wipers 83 to 85, inclusive, there will in this manner be effected the restoration of the switch to normal or zero condition in readiness for a succeeding station selection operation.

In illustrating the application of the present invention there has been chosen for arbitrary illustration the rotary line finder apparatus identified as Strowger step-by-step switches. To those acquainted with exchange office apparatus it will be evident that other forms 01' line finder systems, such as the panel or cross-bar selectors. are equally adaptable for use and that multiple digit selection may be obtained by the application of known circuit arrangements.

While the present invention has been explained I and described with reference to but a single embodiment, it is to be understood nevertheless that numerous variations and modifications may be incorporated without substantial, departure from the present invention. Accordingly, it is not intended to be limited to the specific details of the foregoing specification nor to the particulars of the accompanying drawings except as indicatedin the hereunto appended claims.

What is claimed is:

1. In a telegraph transmission system, a keyboard apparatus comprising a plurality of individually actuable keys, an impulse transmitting means including a rotatable shaft and a set of signal composing contact members controlled thereby, means responsive to the manipulation of any one oi the keys to condition said set of contacts for transmission of code signals and to simultaneously release said rotatable shaft for a single cycle or control of said contacts.

means for causing a predetermined number of consecutive cycles of predetermined code signals comprising a dial manipulable from a normal position to diflerent predetermined extents, a stop mechanism for said dial and movable therewith during the final portion of the movement of the dial to its final setting, means operable by the stop mechanism when so moved for simultaneously depressing one of said keys and for releasing said rotatable shaft for an indefinite number of cycles of control of the contacts, means controlled by the rotatable shaft for each of its control cycles for returning the dial step by step to its original position, and means controlled by the dial when it reaches its original position for disabling said means operable by the stop mechanism.

2. In a telegraph transmitter, key means, impulse transmitting means including a rotatable instrumentality and a set of contact controllers controlled thereby, means controlled by said key means for governing said contact controllers according to the manner of operation of said key means and to simultaneously initiate rotation of said instmmentality for a single cycl of control of said contact controllers, means for causing a predetermined number of consecutive cycles of predetermined code signals comprising a dial manipulable from a normal position to difierent predetermined extents, a stop mechanism for said dial and movable therewith during the final portion of the movement of the dial to its final setting, means operable by the stop mechanism when so moved for simultaneously operating said key means and for initiating rotation of said instrumentality for an indefinite number of cycles or control of said contact controllers, means controlled by the rotatable instrumentality for each of its control cycles for returning the dial step by step to its original position, and means controlled by th dial when it reaches its original position for disabling said means operable by the stop mechanism.

3. In a keyboard transmitter apparatus, a

' cyclically rotatable shaft, a plurality of key levers,

a set of permutation bars controlled by said key levers, a corresponding set of code transmitting contacts, means on said shaft for operating said contacts, means responsive to the manipulation of any one of said keys to condition said contacts in accordance with the setting of said bars and to cause a single cyclic rotation of said shaft for a single cycle or control of said contacts, means for causing a predetermined number oi. consecutive cycles oi rotation of said shaft comprising a dial manipulable from a normal position to difierent predetermined extents, a stop mechanism for said dial and movable therewith during the final portion of the movement of the dial to its final setting, means. operable by the stop mechanism when so moved for simultaneously operating one of said key levers and for releasing said rotatable shaft for an indefinite number of cycles of control of said contacts, means controlled by the rotatable instrumentality for each oiits control cycles for returning the 'dial step by step to its original position, and means controlled by the dial when it reaches its original position for disabling said means operable by the stop mechanism. LOUIS M. PO'I'IS. 

